Hours: Grounds open until 8 p.m. or sunset, whichever is later, Apr.-Oct.; until 4:30 or sunset, whichever is later, rest of year. Visitor center open Mon.-Sat. 8-6, Sun. 10-6, Apr.-Oct.; Mon.-Sat. 8-4:30, Sun. 10-4:30, rest of year. Library open Mon.-Fri. 8-4:30, Sat.-Sun. 11-4:30. Arboretum closed Thanksgiving and Christmas; phone ahead for holiday hours for other facilities.